As an example of printers for a facsimile, a register, and so forth, there has been used a thermal printer provided with a thermal head and a platen roller, for performing printing on a recording medium such as heat-sensitive paper, a thermal transfer ink ribbon, or plain paper. As a thermal head mounted in such a thermal printer, there is known the one having a plurality of heat generating elements arranged on a head substrate and a control element disposed on the head substrate, for controlling the driving of the heat generating element. The platen roller has the function of pressing a recording medium such for example as heat-sensitive paper against the heat generating elements. In the thermal printer thus constructed, the heat generating elements are caused to generate heat in accordance with a desired image, and a recording medium is pressed against the heat generating elements by the platen roller. In this way, heat generated by the heat generating element can be transmitted satisfactorily to the recording medium. With the repetition of such process steps, the desired image can be printed onto the recording medium.
Some thermal heads of this type are installed with a thermistor configured to detect thermal head temperature. An example thereof is disclosed in Patent literature 1. In the case of conducting temperature detection with such a thermistor, there is used a detector configured to detect variation in resistance value of the thermistor as variation in the magnitude of voltage or electric current. In this case, however, the influence of noise becomes more significant with an increase in the distance of signal transmission. In this regard, in the case where the detector is mounted on the head substrate to achieve a decrease in the transmission distance, the possibility arises that, due to heat generated by the heat generating element, the rated junction temperature of a semiconductor device inside the detector will be exceeded with a consequent operation abnormality, or that the heating/cooling temperature variation is so great that the service life will be shortened.
Such a problem associated with the influence of the transmission distance and the influence of heat generated by the heat generating element is not encountered only in the case of thermistor-based temperature detection. The problem could occur in a detector which employs a semiconductor device configured to convert a signal which is involved directly or indirectly in driving of the heat generating element.